Many echinoderms, such as sea cucumbers, share the ability to rapidly and reversibly alter the stiffness of their connective tissue. In the case of sea cucumbers, this morphing occurs within seconds and creates considerable survival advantages. A series of recent studies on the dermis of these invertebrates has provided evidence that this defense mechanism is enabled by a nanocomposite structure in which rigid, high-aspect ratio collagen fibrils reinforce a viscoelastic matrix of fibrillin microfibrils. The stiffness of the tissue is regulated by controlling the stress transfer between adjacent collagen fibrils through transiently established interactions. These interactions are modulated by soluble macromolecules that are secreted locally by neurally controlled effector cells. The dermis of the Cucumaria frondosa and other sea cucumber species represents a compelling model of a chemo responsive material in which a modulus contrast by a factor of 10 (˜5 to ˜50 MPa) is possible.
In view of the above, it would be desirable to provide artificial dynamic materials that exhibit stimuli-responsive mechanical properties similar to the abilities displayed by many echinoderms, especially materials that could be used in biomedical applications.